This invention relates to a thermal head control device arranged to prevent the deterioration of a printing quality caused by the overheating of a thermal head when a thermal printer carries out a continuous printing, and more particularly, to a thermal head control device having a function capable of shortening a period for energizing heat elements of the thermal head and controlling the period so as not to be lowered below a predetermined value.
Conventionally, when a thermal printer carries out a continuous printing, there is a problem that a thermal head is overheated and printing quality is deteriorated. Then, there is a device wherein when the same heating element provided with a thermal head is continuously energized, an energizing period therof is shortened. Since, however, a temperature increase caused by the energizing of one heating element affects heating elements disposed in the vicinity of it, there is a problem in a continuous printing that a printing quality is deteriorated because of the overheating of the thermal head even if the same heating element is not continuously heated.
Therefore, as disclosed in Japanese Utility Model Provisional Publication SHO62-157233, a device is proposed wherein dot densities are counted and totaled, and a period for energizing all heating elements is shortened by a result of the count.
The device disclosed in the above Japanese Utility Model Provisional Publication SHO62-157233, however, has a problem in that control is complex, processing time is increased, and high speed printing is difficult because dot densities are counted and totaled.
Further, with this conventional device, since there is a temperature increase by the energizing of heating elements and heat radiation from a thermal head itself, the temperature increase in the thermal head is gradually equilibrated with the heat radiation therefrom when an energizing period of the device is continuously shortened. If the energizing period is further shortened in this state, the temperature of the thermal head begins to fall. As a result, there are problems that the temperature of the thermal head is excessively low, and thus printing is made too light, and in some cases characters become blurred or are not printed. In particular, in the modern society where information is highly utilized, a printer and the like are required to carry out a high speed and high quality printing so that the solution of the above problems is desired.